The invention relates to a dressing device for profiling grinding wheels for the form grinding of helically toothed involute cylindrical gears, of the kind that comprises an arcuate roller guide, a rolling straight edge, which is capable of rolling on the roller guide, a tool-holder slide guideway, which is helically adjustable to correspond to the base helix angle of the toothing to be ground and can have an involute movement imparted to it from the said straight edge, a tool-holder slide, which is displaceable along the tool holder slide guideway and carries a pointed or tipped dressing tool, and a pivotable member which, with the rolling movement of the rolling straight edge, participates in its pivotal movement about the axis of the roller guide but not in its rectilinear rolling movement component.
With one known dressing device of this type (German Patent Specification No. 1,050,152), the pivotable member is T-shaped in form and comprises a longitudinal beam and a transverse beam. Mounted on the transverse beam are rollers which run on the rolling straight edge in its longitudinal direction, so that the transverse beam always extends parallel to the straight edge and the longitudinal beam always extends perpendicular to the straight edge. The longitudinal beam has a guideway which extends along it, that is to say, at right-angles to the straight edge, and which accommodates a bearing block which is adjustable by means of a screw along the guideway. A crank gear, which converts the pivoting movements of the pivotal member into displacements of the tool-holder slide is a crank-grinding gear with a crank, a rocker arm and a lifting rod. The crank is mounted on the bearing block so as to be incapable of displacement relative thereto and is so connected by a parallel guide linkage to a fixed structural part of the dressing device that it is only capable of being moved parallel to itself. The rocker arm is guided so as to be displaceable longitudinally on two slider blocks, one of which is rotatably mounted on one end of the crank and the other of which is rotatably mounted on the bearing block. An end of the rocker arm remote from the bearing block is pivotally connected to the lifting rod, which is guided for displacement on the straight edge parallel to its longitudinal direction and which carries a pin extending at right-angles to the plane of the straight edge. The tool holder slide is directly guided on the straight edge and comprises a transverse arm on which the pin of the lifting rod bears for displacing the tool holder slide.
This known dressing device is susceptible to errors because of the many moving parts of the crank grinding unit (see article by G. Niemann and J. Looman "Abrichtgerate fur das Profilschleifen von Schragstirnradern" VDI Journal 102 (1960), No. 6, 21st February, pages 231-238). The error susceptibility of this known crank grinding gear is mainly due to the fact that the angle between the crank and the rocker arm is considerably altered with the rolling movement and the swinging of the pivotal member that is associated therewith, so that there is a danger of jamming occurring. Furthermore, the crank grinding gear is difficult to fit, because the longitudinal beam of the pivotal plate is necessarily comparatively long. Moreover, this known dressing device can only be used with a specific rolling cylinder; it cannot be so modified that the diameter of the base circle is continuously adjustable.
Accordingly, the invention has for its object to design a dressing device of the type initially described and having a simple and robust crank gear, which is capable of guiding the tip of the dressing tool on a curve which corresponds with sufficient accuracy to the common line of contact between one tooth flank of an involute cylindrical gear and a grinding wheel which is grinding the said tooth flank.